Field
The disclosed concept pertains generally to circuit protection devices, such a circuit breakers having configurable electronic trip units and motor protectors, and, more particularly, a simplified method of setting the trip parameters of circuit protection devices.
Background Information
Circuit interrupters, such as circuit breakers, are generally old and well known in the art. Circuit breakers are used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload condition or a relatively high level short circuit or fault condition.
Small circuit breakers used for residential and light commercial applications (in load centers and panelboards) are commonly referred to as miniature circuit breakers (MCBs). Circuit protection in MCBs is typically provided by a thermal-magnetic trip device. This trip device includes a bimetal, which heats and bends in response to a persistent overcurrent condition. The bimetal, in turn, unlatches a spring powered operating mechanism, which opens the separable contacts of the circuit breaker to interrupt current flow in the protected power system.
Another type of circuit breaker, known as a molded case circuit breaker (MCCB), is typically used in switchboards and switchgear. MCCBs typically include a pair of separable contacts per phase. The separable contacts may be operated either manually by way of a handle disposed on the outside of the case or automatically response to an overcurrent condition. Typically, such circuit breakers include: (i) operating mechanism which is designed to rapidly open and close the separable contacts, and (ii) a trip unit which senses overcurrent conditions in an automatic mode of operation. Upon sensing an overcurrent condition, the trip unit trips the operating mechanism to a trip state, which moves the separable contacts to their open position.
It is well known to employ trip units which detect various types of overcurrent trip conditions and provide various protection functions, such as, for example and without limitation, a long delay trip, a short delay trip, an instantaneous trip, and/or a ground fault trip. The long delay trip function protects the load served by the protected electrical system from overloads and/or overcurrents. The short delay trip function can be used to coordinate tripping of downstream circuit breakers in a hierarchy of circuit breakers. The instantaneous trip function protects the electrical conductors to which the circuit breaker is connected from damaging overcurrent conditions, such as short circuits. As implied, the ground fault trip function protects the electrical system from faults to ground.
The earliest electronic trip unit circuit designs utilized discrete components such as transistors, resistors and capacitors. More recently, designs, such as disclosed in U.S. Pat. Nos. 4,428,022; and 5,525,985, have included microprocessors, which provide improved performance and flexibility. These digital systems sample the current waveforms periodically to generate a digital representation of the current. The microprocessor uses the samples to execute algorithms, which implement one or more current protection curves.
Electronic trip units have various settings (commonly referred to as trip parameters or trip settings) which can be adjusted to change the behavior of the electronic trip unit (i.e., to specify one or more of the long delay trip, short delay trip, instantaneous trip, and/or a ground fault trip functions). Several known electronic trip units include an interface panel which is used to adjust the trip parameters of the electronic trip unit. One known electronic trip unit includes an interface panel having five rotary switches, two light emitting diodes (“LEDs”), and one test port which are used to adjust the trip parameters of the electronic trip unit. Each component on the electronic trip unit interface panel increases the cost of the electronic trip unit.
In addition, configuring the trip parameters of a circuit breaker can be a difficult task. Often, the trip parameters are left in the most protective levels (factory default) until a trip occurs. In servicing after a trip, the trip parameters are often set to the least protective levels out of ignorance and a desire to avoid another trip.
There is thus a need for a mechanism for configuring the trip parameters of a circuit interrupter which reduces the cost of the electronic trip unit while at the same time allowing settings to be established which better match the application (avoid nuisance trips but protect for a real fault) without requiring a detailed knowledge of circuit interrupter operation.